Adhesives have been used in the wood industry for many years. Uses include the lumber industry, the aggregated fibre board industry, the medium density fibreboard (MDF) market, and the oriented strand board (OSB) market. The chemical composition of wood adhesives varies greatly, but the most widely used adhesives are based upon phenol formaldehyde, urea formaldehyde, urea-melamine formaldehyde, and isocyanate such as polymeric diphenyl methane diisocyanate (pMDI).
pMDI adhesives, in particular, are popular in the USA. pMDI adhesives are normally formed by reacting diphenyl methane diisocyanate with a polyether polyol such as polypropylene glycol. One of the advantages of pMDI adhesives is that the cure mechanism relies upon the moisture content of the wood reacting with free NCO groups in the adhesive to form polyurea, which differs from the other major adhesives in that for most applications heat and pressure is not required to develop a mechanically acceptable joint. However, one of the limiting factors which prevents greater use of pMDI adhesives, when compared, for example to phenol formaldehyde based resins, is their performance under wet conditions. An improvement in the hydrolytic stability of pMDI based adhesives, whilst at least maintaining the adhesive property, is required to significantly increase the use thereof.